Activation of complement by a monoclonal cryoglobulin associated with cold urticaria

A patient subject to cold urticaria had a monoclonal (K type) IgG cryoglobulin with which passive transfer of local cold urticaria to normal recipients could be accomplished. The participation of the complement system was evidenced by a drop in hemolytic complement titer in serial samples of the patient's serum after production of cold urticaria. The cryoglobulin had the following properties attributable to C1 esterase: (1) It inactivated C4 in heated serum; (2) it hydrolyzed N-acetyl-L-tyrosine ethyl ester (ALTEe); (3) the hydrolysis of ALTEe was blocked by purified C1 esterase inhibitor. However, the cryoglobulin failed to transfer hemolytic C1 activity to sensitized red blood cells. Thus, a unique interaction between monoclonal IgG cryoglobulin and C1 has been described.